Background Risks of thyroidectomy for multinodular goiter (MNG) in older and frail patients are unclear, particularly regarding hematoma and recurrent laryngeal nerve (RLN) palsy. Methods MNG patients undergoing total thyroidectomy were reviewed in the ACS-NSQIP procedure-targeted database (2016)(2017). Outcomes were analyzed between adult (age\65), older-adult (age C65 and\80), and oldestold (age C80) patients. Five-factor modified frailty index (mFI-5) was calculated based on functional status, diabetes, COPD, CHF, and hypertension, and used in comparative analyses. Results A total of 2189 adult, 635 older-adult, and 59 oldest-old patients were included. Compared to adult patients, older-adult and oldest-old patients had higher mFI-5 C0.4 rates (14% vs. 22% vs. 31%, respectively, p \ 0.001). The overall complication rate was 17.0% and similar between groups; however, oldest-old patients had higher rates of surgical site infection (3.4% vs. 0.3% vs. 0.4%), pneumonia (5.1% vs. 0.3% vs. 0.2%), and readmission (10.2% vs. 2.4% vs. 2.6%) compared to older-adult and adult patients, respectively (p \ 0.05). On multivariable analyses of thyroidectomy-specific complications, mFI-5 C0.4 (OR 2.5, 95%-CI 1.4-4.4) and bleeding disorder (OR 4.6, 95%-CI 1.3-16.3) were predictive of hematoma, whereas vessel-sealant device usage (OR 0.4, 95%-CI 0.3-0.7) was protective. mFI-5 C 0.4 (OR 1.5, 95%-CI 1.1-2.2), bleeding disorder (OR 2.8, 95%-CI 1.04-7.8), parathyroid autotransplantation (OR 1.7, 95%-CI 1.2-2.6), and prolonged operative time (OR 1.4, 95%-CI 1.02-1.8) were predictive of RLN palsy. Age was not a significant predictor of hematoma or RLN palsy. Conclusions Patients C80 years old are at increased risk for systemic complications and readmission after thyroidectomy for MNG. Frailty index better risk-stratifies patients than age for thyroidectomy-specific complications.